445311ee

feat(font): glyph atlas with row-based packing

a73x 2026-04-08 06:20

Commit message

feat(font): glyph atlas with row-based packing

src/font.zig

@@ @@ -140,6 +140,93 @@ pub const Face = struct { @@
+};
+pub const GlyphUV = struct {
+    u0: f32,
+    v0: f32,
+    u1: f32,
+    v1: f32,
+    width: u32,
+    height: u32,
+    bearing_x: i32,
+    bearing_y: i32,
+    advance_x: i32,
+};
+pub const Atlas = struct {
+    alloc: std.mem.Allocator,
+    width: u32,
+    height: u32,
+    pixels: []u8, // R8
+    cursor_x: u32,
+    cursor_y: u32,
+    row_height: u32,
+    cache: std.AutoHashMap(u21, GlyphUV),
+    dirty: bool,
+    pub fn init(alloc: std.mem.Allocator, width: u32, height: u32) !Atlas {
+        const pixels = try alloc.alloc(u8, @as(usize, width) * @as(usize, height));
+        @memset(pixels, 0);
+        return .{
+            .alloc = alloc,
+            .width = width,
+            .height = height,
+            .pixels = pixels,
+            .cursor_x = 0,
+            .cursor_y = 0,
+            .row_height = 0,
+            .cache = std.AutoHashMap(u21, GlyphUV).init(alloc),
+            .dirty = true,
+        };
+    }
+    pub fn deinit(self: *Atlas) void {
+        self.alloc.free(self.pixels);
+        self.cache.deinit();
+    }
+    pub fn getOrInsert(self: *Atlas, face: *Face, codepoint: u21) !GlyphUV {
+        if (self.cache.get(codepoint)) |uv| return uv;
+        const glyph = try face.rasterize(codepoint);
+        defer face.freeGlyph(glyph);
+        if (self.cursor_x + glyph.width > self.width) {
+            self.cursor_x = 0;
+            self.cursor_y += self.row_height;
+            self.row_height = 0;
+        }
+        if (self.cursor_y + glyph.height > self.height) {
+            return error.AtlasFull;
+        }
+        var y: u32 = 0;
+        while (y < glyph.height) : (y += 1) {
+            const src = glyph.bitmap.ptr + @as(usize, y) * glyph.width;
+            const dst = self.pixels.ptr + (@as(usize, self.cursor_y + y) * self.width) + self.cursor_x;
+            @memcpy(dst[0..glyph.width], src[0..glyph.width]);
+        }
+        const uv = GlyphUV{
+            .u0 = @as(f32, @floatFromInt(self.cursor_x)) / @as(f32, @floatFromInt(self.width)),
+            .v0 = @as(f32, @floatFromInt(self.cursor_y)) / @as(f32, @floatFromInt(self.height)),
+            .u1 = @as(f32, @floatFromInt(self.cursor_x + glyph.width)) / @as(f32, @floatFromInt(self.width)),
+            .v1 = @as(f32, @floatFromInt(self.cursor_y + glyph.height)) / @as(f32, @floatFromInt(self.height)),
+            .width = glyph.width,
+            .height = glyph.height,
+            .bearing_x = glyph.bearing_x,
+            .bearing_y = glyph.bearing_y,
+            .advance_x = glyph.advance_x,
+        };
+        try self.cache.put(codepoint, uv);
+        self.cursor_x += glyph.width;
+        if (glyph.height > self.row_height) self.row_height = glyph.height;
+        self.dirty = true;
+        return uv;
+    }
+};
+test "lookupMonospace returns a valid font path" {
+    var lookup = try lookupMonospace(std.testing.allocator);
+    defer lookup.deinit(std.testing.allocator);
@@ @@ -162,3 +249,24 @@ test "Face rasterizes glyph 'M'" { @@
+    try std.testing.expect(glyph.height > 0);
+    try std.testing.expect(glyph.bitmap.len == @as(usize, glyph.width) * @as(usize, glyph.height));
+test "Atlas packs multiple glyphs and returns UVs" {
+    var lookup = try lookupMonospace(std.testing.allocator);
+    defer lookup.deinit(std.testing.allocator);
+    var face = try Face.init(std.testing.allocator, lookup.path, lookup.index, 14);
+    defer face.deinit();
+    var atlas = try Atlas.init(std.testing.allocator, 512, 512);
+    defer atlas.deinit();
+    const uv_m = try atlas.getOrInsert(&face, 'M');
+    const uv_a = try atlas.getOrInsert(&face, 'a');
+    try std.testing.expect(uv_m.u0 >= 0.0 and uv_m.u1 <= 1.0);
+    try std.testing.expect(uv_a.u0 >= 0.0 and uv_a.u1 <= 1.0);
+    const uv_m2 = try atlas.getOrInsert(&face, 'M');
+    try std.testing.expectEqual(uv_m.u0, uv_m2.u0);
+    try std.testing.expectEqual(uv_m.v0, uv_m2.v0);
+}